Prostate cancer is the second leading cause of cancer death among American men, after lung cancer. Since early 1990s, Focus Surgery, Inc. (FSI) has developed and commercialized the Sonablate TM system, which makes use of a novel technology based on high intensity focused ultrasound (HIFU) for the minimally invasive treatment of prostate diseases. The latest version of the device, the Sonablate TM 500, has been specifically developed and clinically used for minimally invasive image-guided HIFU treatment of localized and recurrent prostate cancer. Following the successful accomplishments of the Phase I study, in this Phase II proposal we plan to refine and enhance the ultrasound imaging, treatment planning, and treatment execution aspects of the current Sonablate TM 500 system for a safe, effective, and minimally invasive prostate cancer treatment. The proposed R & D efforts will minimize side effects such as erectile dysfunction and impotency related to prostate cancer treatment. This goal will be accomplished by the stated specific aims: (1) add Doppler imaging support to aid in the detection of treatment exclusion zones such as neuro-vascular bundles, enhance 2D multi-slice and 3D ultrasound imaging and visualization (2) develop innovative computer-assisted 3D shape models from patient-specific 3D ultrasound data for on-line treatment planning and visualization, (3) develop a full 3D treatment planning tool geared toward both whole and partial (selective) prostate ablation, (4) integrate the new hardware and software enhancements into the Sonablate TM 500 device in preparation for clinical evaluation, and (5) complete an in vivo canine prostate study (both non-cancerous and cancerous prostate models) to evaluate and test the new features. Successful completion of this project, together with currently undergoing prostate cancer clinical trials, will bring the Sonablate TM 500 device to a status ready for widespread clinical use for the safe and minimal side effect treatment of early detected localized (T1 and T2) and recurrent prostate cancer.